Heat Probe

Artist's Concept of InSight Lander on Mars
InSight is the first mission dedicated to investigating the deep interior of Mars. The findings will advance understanding of how all rocky planets, including Earth, formed and evolved.

Taking the Temperature on Mars

The Heat Flow and Physical Properties Probe, HP3 for short, burrows down to almost 16 feet (five meters) into Mars' surface. That's deeper than any previous arms, scoops, drills or probes before it. Like studying the heat leaving a car engine, it measures the heat coming from Mars' interior to reveal how much heat is flowing out of the body of the planet, and what the source of the heat is. This helps scientists determine whether Mars formed from the same stuff as Earth and the Moon, and gives them a sneak peek into how the planet evolved.

HP3
decorative gear graphic


Tech Specs


  • Main Job: HP3 takes Mars' temperature, revealing just how much heat is still flowing out of the interior of the planet.
  • Location: Mounted on the lander deck at launch. Upon landing, the lander's arm picks up HP3 and places it on the surface. The mole then hammers itself under the surface.
  • Mass: Just over 6.5 pounds (about 3 kilograms)
  • Power: A maximum of 2 watts while burrowing underneath the surface.
  • Volume: About 5.3 gallons (20 liters) in total
  • Data Return: 350 megabits over the course of the mission
image of Tilman Spohn
Tilman Spohn
Principal Investigator
German Aerospace Center
(Deutsches Zentrum für Luft- und Raumfahrt, or DLR), Berlin






"We know that Mars' interior is not as warm as Earth’s, but we've never taken the planet's temperature. HP3 will take Mars' temperature, tell us how much heat is leaving the planet, and whether Earth and Mars formed from the same stuff. That's key to learning not only about Mars, but about how all the rocky planets of the solar system formed and evolved."

-- Tilman Spohn
Five Things to Know
Taking the Temperature
Digging Deep
A Sensitive Tail
Flowing Heat
The Stuff of Mars
HP3 takes the temperature of the interior of Mars, much like a thermometer measures a person’s body temperature.
The heat flow and physical properties package has a probe that burrows down as far as 16 feet (5 meters) below the surface. That's deeper than previous instruments to any other planet, moon, or asteroid, which have only ever dug through the upper inch of rock or soil.
Like a mole with a sensitive tail, HP3 pulls a ribbon-shaped cable behind it that's jam-packed full of temperature sensors.
HP3 tells scientists how heat flows inside Mars.
Information from the heat flow package reveals whether Mars and Earth formed from the same stuff, and how active Mars really is today.

Did You Know?

HP3 digs deeper than all previous arms, scoops, drills or probes that have ever studied Mars!

How It Works

Like studying the heat leaving a car engine, HP3 will study the heat coming out of Mars, to shed light on what's producing the heat. It will tell scientists whether Earth and Mars are made of the same stuff, and how heat flows inside Mars.

How Heat Escapes Mars

Planets have heat within them, and some, like the Earth for example, are hotter than others, such as Mars. Hot elements that were present in the material that first formed the planet, and energy left over from the process of planet formation, are the fuel that produces this heat. It gives rise to magnetic fields, mountains, and movement in the crust, which causes quakes. HP3 studies the heat escaping from Mars to determine how fast the "engine" of the planet is running and what's fueling it.

HP3 buries down to almost 16 feet (5 meters) to ensure its measurements remain unaffected by the changes in the seasons. Every 1.5 feet (50 centimeters) the probe puts out a pulse of heat and its sensors watch how the heat pulse changes with time. If the crust material is a good conductor of heat, like metal, the pulse will decay quickly. If it is a poor conductor, like glass, the pulse will decay slowly. This tells scientists how quickly the temperature increases with depth, and how heat flows inside Mars.

Are Earth and Mars Siblings?

Scientists suspect that Mars was born from the same planet-forming material as Earth and the Moon. The heat flow package's measurements will help determine whether this is true. How Mars' fuel, its heat-producing elements, are distributed in the planet today is still an open question. The information from InSight's heat flow package and its seismometer together can help answer this question.